A variety of electronic devices using organic materials such as conducting oligomers or polymers have been proposed. Examples of such organic materials include conducting polymers having a conjugated double bond, such as polyacetylene, and organic compounds having a relatively low molecular weight, such as oligothiophene or phthalocyanine. Those organic materials have .pi. electrons, which are freely movable in a molecule. The mobility of electrons or holes in those materials is an important consideration in the formation electronic devices.
The orientation of molecules or molecular chains is one of the important factors influencing the conductivity of conductive materials.
Conventional methods of orienting organic electronic materials include the following:
natural orientation due to an interaction among molecules or molecular chains that is characteristic of the compounds; PA1 selectively orienting the compounds in the process of forming a conductive polymer by providing a fine groove on a substrate surface and filling the groove with a reaction catalyst disclosed in Japanese Unexamined Patent Publication No. Hei 3-21861; PA1 orienting a conductive polymer by fixing both ends of a wet conductive polymer during the process of forming the conductive polymer through electrolytic polymerization, and PA1 gradually drying and processing the polymer with heat, thus orienting the polymer due to its shrinkage disclosed in Japanese Unexamined Patent Publication No. Hei 2-44607; and PA1 orienting a conductive polymer by fixing both ends of the polymer and mechanically drawing the polymer.
The orientation of a conductive oligomer is generally created by natural orientation due to an interaction among substituents of the molecules or van der Waals force.
Among various electronic devices, field effect transistors (FET) are used as a driving device in a liquid crystal display and the like. Conventional conducting organic materials for the devices include .pi.-conjugated compounds such as polypyrrole, polythiophene, which are disclosed in Japanese Unexamined Patent Publication Hei 3-255669, and oligothiophene compounds, which is disclosed in Gilles Horowitz et al., Molecular Electronics, 7, 85 (1991).
However, it has been difficult for the above-noted conventional technologies to orient large areas of conductive materials or thin films of these materials. When a conductive material is applied to an electronic device, conduction carriers (electrons or holes) should have high mobility without being trapped. However, no good method has been found for orienting oligothiophene as a conductive material.
To solve the above problem, T. Dyreklev proposed the use of polythiophene derivatives mechanically stretched and oriented (Synthetic Metals, 57, 4093 (1993)). However, this procedure provided an insufficiently low mobility of 10.sup.-5 cm.sup.2 /V.s at most. The method of manufacturing devices, for example, FET devices, included adhesion of films mechanically stretched to gate insulating films. This process is difficult to carry out industrially, and the adhesion is unsatisfactory.
A molecular arrangement technique employing a polytetrafluoroethylene (PTFE) oriented film has been used mainly for polymer materials, and its usefulness has been realized. However, the usefulness of the above-mentioned technique for orienting materials which have rigid molecular structures and comparatively low molecular weights, such as conductive oligomers, has not been established.
In order to solve these problems with the conventional materials, the invention applies the above-noted molecular arrangement technique to oligothiophene materials, thus establishing the usefulness of the molecular arrangement technique employing a PTFE oriented film, highly orienting large areas of conductive materials or thin films of the materials, and improving the mobility of conduction carriers (electrons or holes).
The invention provides an improved organic electronic device by improving the orientation of organic materials for increasing the mobility of carriers. Specifically, the invention uses an oligothiophene compound, a polyphenylene vinylene compound, or a mixture of at least two oligothiophene compounds. Those compounds are epitaxially deposited on a PTFE oriented film and oriented.